The present invention relates to hydrostatic bearings, and particularly, but not exclusively, as applied to machine tools.
For high precision machining, it is imperative that the workpiece be held near perfectly stable or be moved through extremely precise motion increments while a tool is operating upon the workpiece, such as, for example, in milling, drilling, or punching operations. Thus, the slide or table upon which the workpiece is positioned must be capable of resisting the high forces imposed upon the workpiece by the tool without deforming or deflecting in any way. At the same time, the slide must be movable along the machine way in a smooth and efficient manner.
A number of different bearing systems have been devised to meet such requirements. Among hydrostatic bearings, a typical example is the classical system in which a high pressure oil film separates two bearing surfaces. The oil is supplied to the bearing by means of a high pressure oil source. It flows through the bearing, dropping in pressure to atmospheric upon exiting from the space between the bearing surfaces.
One disadvantage to such "open" system is that it provides no means of controlling the relative position of the bearing members. There is no feedback which adjusts the flow to the bearings so as to maintain a constant bearing gap. As a result, the stiffness of such system, i.e. the change in oil film thickness brought about by a change in load conditions, is affected by accuracy deviations in the way surfaces, structural deformations due to machine loads, and thermal deformation.
Additionally, no provision is made for the recovery of the hydraulic fluid in an open system. Upon flowing out of the bearing onto the way surfaces, it becomes contaminated and is lost from the system.
It is, accordingly, an object of the present invention to provide a servostatic bearing system which is hydraulically closed and possesses a variable stiffness capability.
Another object of the invention is to provide a servostatic bearing system having a completely closed hydraulic circuit and precise control of stiffness utilizing continuous feedback to the fluid distribution means of pressure changes due to changes in load conditions.
A further object of the invention is to provide a hydraulically closed, variable stiffness bearing system for use with machine tools, such that the bearing system stiffness may compensate for the insufficient stiffness of the other components of the machine tool, producing a machine tool capable of being adjusted to any desired stiffness.
Another object of the invention is to provide a servostatic bearing system for use with machine tools which does not require specially hardened machine way surfaces permits greater manufacturing tolerances in machine components than in machines heretofore known, and minimizes alignment problems in the machine components.
A further object of the present invention is to provide a servostatic bearing system utilizing a minimum number of components, each of simple construction, so that manufacturing costs are kept advantageously low.
Still another object of the invention is to provide a servostatic bearing system utilizing a modular construction which affords maximum ease of assembly and maintenance of the bearing pads.
Other objects and advantages of the invention will become apparent from the description following below.